1. Field of the Invention
The present invention relates generally to a lens control unit, and more particularly to a lens control unit that generates control signals for electrically controlling the focusing and zooming of a lens device for use in a TV camera, or the like.
2. Description of Related Art
A control unit called a zoom rate demand or a focus position demand is used to control a TV lens device in the zooming, focusing, or the like. The control unit (demand) usually has a control member such as a ring and a knob. Manually turning the control member causes a potentiometer, a rotary encoder, or the like, which interlocks with the control member, to output electric signals (control signals) according to the operated amount of the control member. Then, a driving part such as a motor is controlled according to the electric signals to move a lens group in the TV lens device. Thus, the zooming or focusing is performed.
There is also a well-known TV lens device, which is provided with a preset shooting function for instantaneously reproducing the previously-stored focus position and zoom position by operating a button.
When the lens device connected to a focus demand activates the preset shooting function or an auto-focusing function, a position signal outputted from the focus demand is cut off and a lens (e.g., a focus lens) moves to a position indicated by a preset signal or the like. Then, when the preset shooting function or the auto-focusing function is cancelled, the focus lens returns to a position designated by the focus demand. If a subject is focused at the preset position, however, the image may be blurred as soon as the preset shooting function is cancelled.
To address this problem, it is preferable to maintain the state such as the focus position of the lens even if the preset shooting function is cancelled. In this case, the focus position can be prevented from changing due to the cancel of the preset shooting function if an incremental rotary encoder, or the like is used as a position sensor for determining the rotational angle (the turned position) of the control member of the focus demand and if stoppers are formed at both rotational ends of the control member of the focus demand. However, according to this structure, the stopper positions of the focus demand may shift from the ends of the focus lens. Consequently, even if the control member of the focus demand turns to the rotational limit or end, the focus lens cannot reach the end (a proximity end or an infinity end), and an area where the focus cannot be adjusted results.
Japanese Patent Provisional Publication No. 8-313793 pointed out a similar problem. This publication proposed the structure for prohibiting the rotation of the control member when an end detecting means provided in a lens device detects that a lens has reached the end. More specifically, teeth are formed at the outer circumference of a ring member that turns in association with the control member. When the lens reaches the end, a power source such as a motor is run to turn a stopper frame member so that the end of the stopper frame member engages with the teeth of the ring member to thereby stop the control member.
In the lens control apparatus of No. 8-313739, the power source such as the motor must be run to move the stopper frame member forward into the rotatable area of the ring member every time the lens is detected at the end. Therefore, a relatively large amount of energy is used, and the control system is complicated. In addition, the frequent rotation of the stopper frame member deteriorates the durability and causes mechanical troubles.
In view of the foregoing, it is an object of the present invention to provide a lens control unit, which is able to maintain the state of the lens and maintain the relation between the operational limits of the control member in the lens control apparatus and the movement limits (ends) of a lens (e.g. a focus lens) in the lens device if a control function such as a preset shooting function and an auto-focusing function other than the lens control unit is operated and then the control is cancelled, so that the operator can feel the operational limits of the control member at the movement limits of the lens.
To achieve the above-mentioned object, the present invention is directed to a lens control unit for outputting a signal corresponding to displacement of a control member and controlling a position of a lens according to the signal, the lens control unit comprising: the control member; a stopper member for defining an operational limit of the control member; a support mechanism for movably supporting the stopper member; a power source for supplying power to the support mechanism to move the stopper member; and a control part for controlling the power source to move the stopper member so that the operational limit of the control member with respect to a current position of the control member corresponds to a movement end of the lens with respect to a current position of the lens.
According to the present invention, if the operational limit of the control member is displaced from the movement end of the lens after the control function such as the preset shooting function other than the control unit is operated to move the lens, the control part determines the relation between the current position of the lens and the movement end of the lens, and controls the power source to move the stopper member so that the relation between the current position of the control member and the position of the stopper member can correspond to the relation between the current position of the lens and the movement end of the lens. Consequently, the operational limit of the control member can easily correspond to the movement end of the lens.